Effect of the rate of prestretching a peripheral nerve on regeneration potential after transection and repair.

We tested the influence of nerve stretch injury on nerve regeneration after cutting and suturing. An external fixator was used to lengthen the femur, and consequently the sciatic nerve, progressively, by 3 mm/day (5%/day: group I) or 5 mm/day (9%/day: group II). In both groups the total lengthening was 15 mm, corresponding to approximately 23%-28% elongation of the sciatic nerve. Seven days after initiating nerve lengthening, the external fixator was removed and the nerve was transected and sutured. At 2, 4, 6, or 8 weeks after this suturing, semithin sections were prepared from the sciatic and tibial nerves. Although regeneration of nerve fibers was observed beginning at 2 weeks in all groups, nerve regeneration showed a delay only in group II at 6 weeks, when group I showed nerve regeneration as good as in the unstretched control group. Differences in nerve regeneration after nerve lengthening at different rates were considered the result of mechanical nerve injury, nerve degeneration, ischemia, and fibrosis, all made worse with more rapid lengthening. Nerve lengthening at a more moderate rate (3 mm/day) did not appear to compromise regeneration.